As is known, an integrated device or a generic electronic circuit generally comprises a plurality of input/output communication cells, which have the function of communication-interface means and are provided in the form of pads, which are coupled to a corresponding circuit configured for enabling a bidirectional communication (or, alternatively, only a communication in reception or sending of data) from the integrated device to the outside and vice versa. In the following description, the term “communication cell” refers to the pad and to the unidirectional-communication circuit (input or output) or bidirectional-communication circuit (input and output) coupled to said pad.
Communication cells of a known type may be used, for example, for connecting components of an integrated device or of a generic electronic circuit with elements external to the circuit itself (for example, for supplying control signals to the integrated device or to the electronic circuit).
FIG. 1 is a schematic circuit representation of a conventional communication cell 1, of a digital type. The communication cell 1 is of an input/output (I/O) type; i.e., it can function both in the input mode (in this case it receives a signal supplied thereto from outside) and in the output mode (it supplies at output a signal, for example a signal of response to the input signal).
In greater detail, the communication cell 1 comprises an input circuit 6 including a signal-stabilization circuit 8, for example a Schmitt trigger, coupled to an interface node 4 (which is in turn coupled to the pad) from which it receives an input signal, and a buffer circuit 10 coupled between the signal-stabilization circuit 8 and an output port 11 of the communication cell 1. The input signal is generated by an electronic system 5, distinct from the communication cell 1, for example formed on a chip which is different from the chip wherein the communication cell 1 is formed.
The buffer circuit 10 is interfaced via the output port 11 with a generic electronic circuit or with an integrated device 7, for supplying the input signal received at the node 4 to the generic electronic circuit or integrated device 7.
For example, the electronic system 5 may be a test station configured to generate a test signal (i.e., the input signal) for testing the functionalities of the integrated device 7. The communication cell 1 acts as an interface between the test station and the integrated device 7. The test signal is provided to the communication cell 1 through a probe in ohmic contact with the pad coupled to the interface node 4.
The communication cell 1 further comprises a load-driving circuit 2, which, for example, includes a buffer, configured for receiving, via an input port 3 of the communication cell 1, a signal coming from the generic electronic circuit or integrated device 7.
As said, known techniques for carrying out testing of an electronic circuit envisage the use of probes of a mechanical type, configured for contacting respective pads of the communication cell 1. Said mechanical probes may be arranged in direct contact (ohmic contact) with the pad coupled to the external interface 4 of the communication cells 1 for supplying test signals to an electronic circuit or integrated device 7 coupled to the communication cell 1, and acquiring response signals from the circuit or integrated device 7 itself. The response signals may be used to check the operating state of the circuit or integrated device 7 under test. Access to the communication cells 1 by means of mechanical probes, however, may cause damage to the pad of the test communication cell 1, due to the physical contact that is set up between the probe and the corresponding pad. In addition, the use of contact probes may not enable analysis of the real operation of the circuit under test when said circuit operates at high frequency (for example, in the case of RFID devices, devices operating at radiofrequency, etc.).
To overcome the aforementioned disadvantages, contactless probing through capacitive coupling has been provided, for example as disclosed in U.S. Pat. No. 6,600,325, which is incorporated by reference. Document U.S. Pat. No. 6,600,325 discloses a system for capacitively probing electrical signals within an integrated circuit. This system operates by placing a probe conductor in close proximity to, but not touching, a target conductor within the integrated circuit. In this position, the probe conductor and the target conductor form a capacitor that stores a charge between the probe conductor and the target conductor. Next, the system detects a change in a probe voltage on the probe conductor caused by a change in a target voltage on the target conductor, and then determines a logic value for the target conductor based on the change in the probe voltage.
Another non contact tester is provided by U.S. Pat. No. 6,885,202, which is incorporated by reference, in particular for electronic circuits. The non contact tester consists of an electronic circuit and independent scanning head, in combination. The electronic circuit includes a microfabricated wireless I/O cell and means for sending and receiving signals via the wireless I/O cell. The independent scanning head has a wireless I/O cell that is compatible with the wireless I/O cell on the electronic circuit. This enables data to be exchanged with the electronic circuit to confirm proper functioning of the electronic circuit.